The present invention relates to a method of manufacturing methallyl sulfonate, and particularly it relates to a method of manufacturing methallyl sulfonate wherein a dialkyl sulfoxide-sulfur trioxide complex is employed for sulfonation of isobutylene.
Methallyl sulfonate is an important monomer to be combined with acrylonitrile to form a copolymer, and as to the method of manufacturing thereof, there have hitherto been proposed a variety of methods. One of them is a method wherein isobutylene is first chlorinated and then the resulting methallyl chloride is made to react with sodium sulfite. This method, however, is accompanied with a relatively large quantity of sodium chloride as the by-product having a harmful effect on the polymerization of methallyl sulfonate. Another method intended for direct sulfonation of isobutylene wherein reaction between isobutylene and sulfur trioxide is to be effected in a liquid sulfur dioxide at -20.degree.C has been disclosed on page 787 of Bull. Soc. Chim. France (1965). This method, however, is of no practical use inasmuch as it produces a large quantity of isobutylene polymer as the by-product. As the method of sulfonating isobutylene by the use of a certain SO.sub.3 complex, there are known such a method as disclosed on page 978 of J. Am. Chem. Soc. 63 (1941) wherein sulfur trioxide-dioxane complex is to be employed and a method as disclosed in Japanese Pat. Publication No. 41527/1971 wherein sulfur trioxide - alkyl amide complex is to be employed. However, according to the former method, not only is it difficult to maintain the complex stable, but also the accompanying by-products in large quantities remarkably lower the yield of the intended product. As to the latter method, on the other hand, though it is possible to stably maintain the complex employed and effect its reaction with isobutylene, it is defective in that it is indispensable to use excess alkyl amide in effecting said reaction and the methallyl sulfonate produced thereby gets somewhat colored, so that it is not always suitable.
The present invention is intended for improvement of the method of sulfonating isobutylene employing sulfur trioxide - dialkyl sulfoxide complex, and is to provide a method rendering it possible to obtain an uncolored methallyl sulfonate in high yield by virtue of the employment of sulfur trioxide - dialkyl sulfoxide complex. Application of sulfur trioxide - dialkyl sulfoxide complex as the sulfonating agent has so far been tried on special alcohols, and in such cases, the presence of excess dialkyl sulfoxide is indispensable in order to stably maintain the complex. Besides, even when the complex is thus maintained stably, it is impossible to obtain the sulfonate in high yield. But, the inventors of the present invention have found the fact that, said sulfur trioxide - dialkyl sulfoxide complex is suitable for use in sulfonation of isobutylene which is different from ordinary sulfonation reaction in that methallyl sulfonic acid is to be produced through sultone, and employment of this complex for sulfonation of isobutylene followed by neutralization renders it possible to manufacture an uncolored methallyl sulfonate in high yield.